Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $202.77   11.675%   $226.4434   $226.44   $226.45   $226.40  
  Purchase #2 $60.38   9.424%   $66.0702   $66.07   $66.05   $66.10  
  Purchase #3 $41.33   7.806%   $44.5562   $44.56   $44.55   $44.60  
  Purchase #4 $179.82   5.347%   $189.435   $189.44   $189.45   $189.40  
  Purchase #5 $240.94   13.437%   $273.3151   $273.32   $273.30   $273.30  
  Purchase #6 $101.45   5.569%   $107.0998   $107.10   $107.10   $107.10  
  Purchase #7 $129.39   7.444%   $139.0218   $139.02   $139.00   $139.00  
  7 purchase totals = $956.08       $1,045.9415   $1,045.95   $1,045.90   $1,045.90